Cold engine operation has numerous disadvantages. Due the rich fuel mixture which must be burnt, fuel consumption is higher, exhaust is dirtier and contains larger amounts of unwanted pollutants, and, the excess fuel dilutes the oil film lubricating the piston-cylinder surfaces causing excessive wear as well as contaminating the oil. Further, engine-heated water is required to defrost/defog the windshield for best visibility for safe driving. All the above disadvantages are minimized at the preferred engine operating temperature range of about 200–210° Fahrenheit (94–98° C.). Consequently, this temperature should be attained as quickly as possible from cold (cold can be below −40° F., ° C.).
Once the engine has reached operating temperature it thereafter produces large amounts of unwanted waste heat that must be dissipated to prevent overheating. This heat is dissipated both by the radiator and by the surface of the engine into the ram air flow that enters the front grill as the vehicle is driven. At idle or in slow moving conditions there is no ram air flow so the fan switches on and off to create air flow at intervals when needed according to engine temperature sensor signal. However the engine surface now receives hot radiator air and so cannot be cooled as effectively as when driving at speed. Further that hot air unwantedly heats the engine bay components and is then discharged beneath the vehicle's front portion wherefrom a portion of the hot air finds its way back to the front intake. Moreover, during the fan's off interval, the engine bay or underhood compartment receives no cooling air and so the components therein soak up heat and must therefore operate at quite high temperatures. These underhood temperatures can reach critical values in long traffic on hot days. Breakdown of the plastics and electronics in the engine compartment becomes a serious concern. Furthermore the passenger cabin has a forward portion or wall (firewall) which receives this unwanted heat in hot weather. This adds to interior heat which the air conditioner must work harder at to cool down. These anomalies add to the cooling load of the radiator which must therefore be larger, heavier and more expensive. Moreover, the engine bay and its contents, including electronic, electric, computer and numerous plastic components all get very hot reaching temperature well over the boiling point of water (220° F., 105° C.) and so must be made of select, expensive materials to withstand the high temperatures.
Future vehicle development plans include attaching more related components directly on the engine to allow complete package testing. This is expected to further raise underhood component temperature and therefore their cost.